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Researching backup units or UPS often means learning lingo that you don’t use in everyday life. Volts? Phase? Single Phase? Three Phase? Don’t worry we put this guide together to make things easier.

Alternating Current

Commonly referred to as AC. It is the way the raw power is delivered to you, as generated, by your utility company. AC takes the form of a sinusoidal waveform which changes in amplitude and direction a fixed number of times per second.

AC is the opposite of DC, and was chosen because it can be sent over many miles by the utility company with relatively low line losses.

Direct Current

Commonly referred to as DC. It is the same type of current that is in a battery. The current is direct, constant and flows from negative to positive.

It is only suitable for transmission over short distances. DC is the opposite of AC

Frequency

Frequency only applies to AC, and is the number cycles per second that the sine wave repeats itself. Also referred to as Hertz (abbreviated Hz).

In North America the frequency is 60Hz. In the rest of the world it’s 50hz.

Volts

The measure of electrical potential that is available for use. Look at it like pressure in your water pipe. It’s always there, just waiting for someone to open the faucet. In the US, the standard residential voltage is 120V. Commercial voltage is generally 208V or 480V

Watts

This is the measure of true Power, and in and AC System it is similar to KVA, with one, very important, critical difference. Power Factor. An explanation of Power Factor is beyond the scope of this blog, but suffice to say it is a rating determined by your load, and then applied in the calculation to determine KW, which for a three phase system is V * A * 1.73 * Pf Power factor in a perfect system will be 1, and if so KVA = KW (also known as unity) In real life the Power factor is rarely one, and is typically somewhere between .9 to .97. In practice , it acts as a de-rating factor, because the typical UPS can deliver less KW than KVA.

Amps

The actual flow, or movement of electrons which is also known as current. The flow of electrons performs a useful task such as lighting a light, turning a motor, or powering a computer. Using the example above under voltage, current would be the flow of water that comes out of the faucet, and is dependent upon how much you open the faucet and the pressure behind it.

KVA

Thousands (Kilo) or Volt Amps. If your UPS operates on 120 Volts and can deliver 10 Amps then the UPS is rated at 1200 Volt Amps OR 1.2KVA (1.2 Thousand Volt Amps).

In single phase systems KVA = V * A

In three phase systems the formula is V * A * 1.73 (the square root of 3).

Important Note: KVA is apparent power, and doesn’t tell the full story of your UPS’s capacity.

Phase

This refers to voltage and defines the number of input wires supplying voltage that are connected to the device. Each wire carrying voltage is sometimes referred to as a “Hot”.

Single Phase

The 120V outlets in your house are all single phase. This means there is one “Hot” wire supplying power to the load. Single phase is used in residential, and low power commercial applications. Single phase UPS’s are small desktop or rack mount systems, and range from 300VA to about 10KVA. Typical manufacturers are APC and Xtreme Power Conversion

Three Phase

Commercial voltage is generally 3 phase, which means there are three separate wires connected to a device each supplying 120V, or a different voltage. Essentially 3 “hots” Three Phase Power is used in Commercial and Industrial applications, and delivers high power. Three Phase UPS’s are larger systems that power many racks of equipment, to large data centers. Three Phase UPS’s will start at around 10KVA and can be as large as 1100KVA. The Eaton 9355 is a great example of a three phase UPS.

Hopefully you found this guide helpful.

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